Thread: Compression and a/f ratio questions

Hi, I just finished my det swap into my nx2k. It runs decent but doesn't feel as quick as it should be. Feels slower than a buddys g20 that has the same motor and upgrades, and my car is stripped out and a lot lighter.
First, I checked my compression and it was 120 all the way across the board. The comp tester I used has measured low compression on my brother's low mileage mazda 323 gtx as well. So i'm not sure if I just have a bad comp tester or we just have several cars with bad piston rings.
Any ideas what else I could do to check to see if my rings are bad? And what compression are other people putting out on here?
And second, I just got my wideband put in and under full boost, i'm getting a/f numbers in the mid to low 10's to 11's. And also, when i watch my boost gauge, it'll will go up to 9-10 quickly, and quickly drop to as low as 5psi sometimes until I let off. I have my boost controller set to 10psi. I'm running a Greddy profec e-01 boost controller as well.
Thanks

compressions for a det range from 150-160psi
afr's are rich in the 10s, unless in the mid 11s like u said then id keep them right there

it varies but usually i see 10's every time i boost hard.
How do I make them better? Change the timing?
That's another problem i'm having. My timing is all the way advanced and it's still running rich. I compared it to a friend that has the same motor as mine even bought from the same importer. His has past half way on the more retarded side.
Any idea what this could be? Bad dizzy? Could it be 180 degrees off?
Thanks

Did you do the test right? Are those hot or cold numbers? Did you pour some oil into the cylinders to see if the pressure went up? Did you try another gauge? All of the questions will help you figure out the problem.

7 psi is stock for a det..remove the b/c and see if it holds 7psi till 6k or so.did u prime the motor before starting?dry/wet compression test and see if u can get a leakdown tester..lastly pressure test ur intercooler pipes for a leak

I still need to get hold of another gauge and try putting some oil in the cylinders. How much should I put in?
I did not prime the motor before starting? Should I have? And i've been driving the car for a couple weeks now too.
Dry compression test. And I did it hot, but I forgot to unplug the injectors when I did it, but by the time I remembered that and unplugged them it was alot colder, and it only went up mabye 4..

Any idea though why my timing is all the way advanced and still running rich?

if you did not have the car in timing mode the ecu does not know the timing has been changed.

here is the procedure to do a comp test. if the numbers are still low put a few table spoons of oil in and retest.

The proper way to do a compression test on a nissan is as follows.
1) warm car to normal operating temp(not to hot or to cold)
2) remove fuel pump fuse
3) start car and allow fuel pump lines to be cleared
4) attempt to start car a few times after it stalls
5) remove all spark plugs
6) disconnect distributor at harness
7) Hold the gas pedal down
8) crank car until the highest reading is reached
9) repeat on each cylinder

its not your compression if all of the numbers are close to eachother. its your tune and your timing is messed up. did you check for boost leaks?

Why does boost fall to 5 psi? Check your boost controller settings and match them to your turbo. If stock det then it's internal wastegate.

I'm sure that greddy should have some switches or something to set up for that type of turbo setup.

That timing should be horribly set with the distributor all advanced (or is it all retarded? Did u check with a timing gun and did the timing mode dance?). Or the chain skipped a tooth on the cam gears...